The present disclosure relates to electronic memory devices based on electric field programmable films. More particularly, the present disclosure relates to electronic memory devices that exhibit bistable behavior.
Electronic memory and switching devices are presently made from inorganic materials such as crystalline silicon. Although these devices have been technically and commercially successful, they have a number of drawbacks, including complex architecture and high fabrication costs. In the case of volatile semiconductor memory devices, the circuitry must constantly be supplied with a current in order to maintain the stored information. This results in heating and high power consumption. Non-volatile semiconductor devices avoid this problem but have reduced data storage capability as a result of higher complexity in the circuit design, which results in higher production costs.
Alternative electronic memory and switching devices employ a bistable element that can be converted between a high impedance state and a low impedance state by applying an electrical voltage or other type of input to the device. Both organic and inorganic thin-film semiconductor materials can be used in electronic memory and switching devices, for example in thin films of amorphous chalcogenide semiconductor organic charge-transfer complexes such as copper-7,7,8,8-tetracyanoquinodimethane (Cu-TCNQ) thin films, and in certain inorganic oxides in organic matrices. These materials have been proposed as potential candidates for nonvolatile memories.
A number of different architectures have been implemented for electronic memory and switching devices based on semiconducting materials. These architectures reflect a tendency towards specialization with regard to different tasks. For example, matrix addressing of memory location in a single plane such as a thin film is a simple and effective way of achieving a large number of accessible memory locations while utilizing a reasonable number of lines for electrical addressing. Thus, for a square grid having n lines in two given directions, the number of memory locations is n2. This principle has been implemented in a number of solid-state semiconductor memories. In such systems, each memory location has a dedicated electronic circuit that communicates to the outside. Such communication is accomplished via the memory location, which is determined by the intersection of any two of the n lines. This intersection is generally referred to as a grid intersection point and may have a volatile or non-volatile memory element. The grid intersection point can further comprise an isolation device such as an isolation diode to enable addressing with reduced cross-talk between and among targeted and non targeted memory locations. Such grid intersection points have been detailed by G. Moore, Electronics, Sep. 28, (1970), p. 56.
Several volatile and nonvolatile memory elements have been implemented at the grid intersection points using various bistable materials. However, many currently known bistable films are inhomogeneous, multilayered composite structures fabricated by evaporative methods, which are expensive and can be difficult to control. In addition, these bistable films do not afford the opportunity for fabricating films in topographies ranging from conformal to planar. Bistable films fabricated using polymer matrices and particulate matter are generally inhomogeneous and therefore unsuitable for fabricating submicron and nanometer-scale electronic memory and switching devices. Still other bistable films can be controllably manufactured by standard industrial methods, but their operation requires high temperature melting and annealing at the grid intersection points. Such films generally suffer from thermal management problems, have high power consumption requirements, and afford only a small degree of differentiation between the “conductive” and “nonconductive” states. Furthermore, because such films operate at high temperatures, it is difficult to design stacked device structures that allow high density memory storage.
Accordingly, there remains a need in the art for improved electric field programmable bistable films that are useful as subsystems in electronic memory and switching devices, wherein such films can be applied to a variety of substrates and produced with a variety of definable topographies. Further, there is a need for electronic memory and switching devices comprising electric field programmable bistable films that can be produced more easily and inexpensively than known devices, that offer more useful differentiation between low conductivity and high conductivity states, that have reduced power and thermal requirements and that can be stacked in various configurations to fabricate electronic devices of higher density.